Proportional Ventilatory Support: A Comparison of Proportional Assist Ventilation,Proportional Pressure Support and Proportional Pressure Ventilation

Background:

Proportional ventilatory support (PVS) refers to modes of ventilation that provide support that is proportional to the patient's inspiratory effort. Research has shown that PVS improves patient ventilator synchrony. Several ventilators are now available that provide a type of PVS. The purpose of this study was to evaluate proportional assist ventilation (PAV+) on the PB 840 and PB 980, proportional pressure ventilation (PPV) on the Respironics V60, and proportional pressure support (PPS) on the Drager V500, using the IngMar Medical ASL 5000 at three different inspiratory efforts (Pmus).

Methods:

The ASL was set to simulate a COPD lung model: compliance 59 mL/cm H₂O; resistance in 22 cm H₂O/L/s; resistance out 18 cm H₂O/L/s; frequency 14 breaths/min; Pmus 12 cm H₂O. Ventilator settings: PAV+ % Supp 25%, 45%, and 65%, Esens 3 L/min; PPV 25%, 45%, and 65%, Max E 17 cm H₂O/L, Max R 20 cm H₂O/L/s; PPS flow assist 25%, 45%, and 65% of the averaged resistance, volume assist 25%, 45% and 65% of the elastance, inspiratory termination 25%; PEEP 7 cm H₂O. Each ventilator was connected to the ASL using a 7.5 mm ETT. After the ventilator was connected, the mode was run at ventilator support (VS) 25%. The ventilator was given one minute after the change had been made to stabilize; data was gathered for an additional minute using the automated ASL software. Next VS was increased to 45% and 65%, following the same procedure. Then, Pmus was increased to 18 and 24 cm H₂O, gathering data as described, at each level of VS.

Results:

As VS increased, tidal volume (V_T) and peak inspiratory pressure (PIP) increased on all ventilators. As VS increased, time to trigger (TT) decreased on all ventilators. As Pmus increased, TT increased. On the PB 840, PB 980 and V500, as VS increased, inspiratory time (Ti) increased; conversely, on the V60 as VS increased, Ti decreased. The PB 980 had the highest average Ti, V_T, PIP, and TT. Ti on the PB 980 increased due to multiple inspiratory pauses, which resulted in AutoPEEP. The V60 had the shortest TT.

Conclusions:

This study demonstrated that PAV+, PPV, and PPS each provide an increase in V_T and PIP as patient effort or VS increases. Using PPV and PPS requires the clinician to know the resistance and elastance of the lung. Clinicians need to be careful to input the value for elastance, not compliance. Further research needs to compare PVS in patients to determine the clinical benefit of each mode.

Pmus 18 cmH2O